We have remote VPN through a Cisco firewall. It works fine for most users. It’s a little slow of course. However, we have one user who remotes in to troubleshoot issues with PLC’s (this is a manufacturing facility). He has a hard time staying connected to the PLCs. Otherwise, his VPN works fine. Are there special considerations for VPN when remoting to PLCs?
Like most networking equipment, PLCs achieve connectivity via IP communication. As far as I know, there is no special requirement for such communication, either on the LAN or over the VPN. Some things that you might want to examine include:
- What is the internal LAN communication with the PLCs like? From a PC in the local LAN, is connectivity stable?
- Where does the VPN terminate? On the Cisco firewall local to the PLCs? Can you test the communication between the firewall IP address/subnet and the subnets that the PLCs are connected to?
- When you say he has a hard time staying connected, what kind of connection is being made? HTTP? Does he have to login again or is the connection simply intermittent? Can you continually ping to the PLC’s IP without problems? Is it a L3 problem or an application problem?
- Is the problem there for all PLCs or just some of them?
These are some of the questions that may help zero in on the specific problem being experienced. Let us know some of the results of these tests so that we can help further in the troubleshooting process.
I hope this has been helpful!